Slow-growth disbond and delamination damage of a bonded composite-metal joint under fatigue loading

Abstract

This study investigates the slow-growth damage behaviours of bonded CFRP-Al hybrid double-lap joints. Static tensile tests were performed to evaluate the residual strength of partially disbonded or delaminated joints. Fatigue tests were conducted at a practical load level based on static joint strength and safety factor requirements to measure fatigue life and crack growth rates. Finite element models were developed and calibrated using experimental residual strengths and the characteristic distance method and then employed to calculate the residual strengths and energy release rates as functions of crack lengths. The extended finite element method and virtual crack closure technique were both applied. The combination of experimental crack growth rates and numerical energy release rates yielded a modified Paris law, which was used to predict the fatigue life of the double-lap joints with gap region delamination. The fatigue test results revealed slow-growth delamination behaviour within the double-lap joint specimens with pre-embedded gap region delamination cracks. Following observations of crack migration from gap region disbond to first ply delamination, finite element analysis revealed the interaction that arises from disbond-delamination crack migration, with delamination growth remaining dominant and disbond growth significantly reducing. The fatigue life prediction for gap region delamination yielded good agreement with experimental joint fatigue life. This study implemented the previously proposed framework for assessing slow-growth damage behaviours of adhesively bonded composite joints.